Addressable monolithic multi-wavelength light sources, especially laser arrays that can simultaneously emit different wavelength light from different elements in the array are useful in a variety of applications, such as color printing, full color digital film recording, color displays, and other optical recording system applications.
In U.S. Pat. Nos. 4,925,811, 4,955,030 and 5,039,627, Menigaux et al. describe various terraced semiconductor layer structures having stacks of alternate confinement layers and active layers. Each active layer in the stack has a different composition and is capable of emitting light of a different wavelength. A desired number of laterally spaced PN junctions are formed by localized introduction and diffusion of a p-type impurity, the different PN junctions being made in the vicinity of different active layers in the stack. The resulting structures can emit, either simultaneously or independently, as desired, different wavelength light beams from the array.
In U.S. Pat. No. 4,831,629, Paoli et al. describe laser arrays that are characterized by nonuniform current pumping across the arrays. The nonuniform current distribution among the several laser emitters of the array is brought about, for example, by different current confinement or stripe widths or by some other nonuniform contact configuration. The different pump current and carrier densities across the array result in different increments of band filling in the active region's quantum well structure, thereby causing individual laser emitters to operate at different emission wavelengths.
In U.S. Pat. No. 4,993,036, Ikeda et al. describe a semiconductor laser array having a double quantum well active region in which the two quantum well layers have different energy gaps, and, consequently, different oscillation wavelengths. There are also provided two adjacent pairs of grating reflectors, each pair having a grating pitch that is tuned to reflect a different one of the two oscillation wavelengths of light. Arrays having more than two quantum well layers, each with a different energy gap, and having more than two sets of wavelength selective reflectors, are also suggested.
In U.S. Pat. No. 4,951,293, Yamamoto et al. describe a semiconductor laser and a frequency doubling optical nonlinear device, both mounted on a submount to form a visible laser source. The nonlinear device can have a plurality of parallel waveguides for receiving light beams from a semiconductor laser array.
An object of the invention is to provide monolithic multi-wavelength semiconductor laser arrays.